Thermosetting isocyanate adhesive comprising a rosin-based tackifying agent, methods and uses thereof

Abstract

The present disclosure relates to a thermosetting isocyanate adhesive composition comprising a tackifying agent comprising a rosin ester, the use of a rosin ester as a tackifying agent of a thermosetting isocyanate adhesive, preferably an initial tackifying agent, wherein the hydroxyl number of the rosin ester is below 1 mgKOH / g; the acid number of the rosin ester is below 4 mgKOH / g; and wherein the rosin ester is liquid at a temperature greater than -5 °C. A tackifying agent, preferably an initial tackifying agent, comprising a rosin ester with said characteristics, resins and articles comprising the described rosin ester, as well as the method of preparing said ester, are also described in the present disclosure.

Description

D E S C R I P T I O NTHERMOSETTING ISOCYANATE ADHESIVE COMPRISING A ROSIN-BASED TACKIFYING AGENT, METHODS AND USES THEREOFTECHNICAL FIELD

[0001] The present description concerns a tackifying agent, preferably an initial tackifying agent, comprising a rosin ester resin and its use as a tackifying agent for isocyanate adhesives.BACKGROUND

[0002] The chipboard and wooden laminate industry uses thermosetting resins as a binder for wood particles and laminates. By volume, the most commonly used resin continues to be urea-formaldehyde (UF) resin; however, this type of resin encompasses some technical problems such as hydrolysis and release of formaldehyde.

[0003] Isocyanate adhesives are a type of adhesive that relies on the reactivity of isocyanate groups (-NCO) to form strong and durable bonds through chemical reactions with compounds containing active hydrogen atoms, such as polyols, amines, or water. These adhesives typically consist of one or more components, where the isocyanate component reacts with the other components to form a polyurethane or polyurea network. Isocyanate adhesives are known for their excellent adhesion to a wide variety of substrates, including metals, plastics, wood, and composites.

[0004] In particular, isocyanate / polyurethane prepolymer systems, refer to adhesive systems composed of isocyanate-terminated prepolymers, which are intermediate products formed by the partial reaction of isocyanates with polyols, designed to further react with additional polyols or other reactants upon application to form polyurethane polymers. They are utilized in various applications including automotive, construction, footwear, woodworking, and industrial manufacturing, offering excellent adhesion, flexibility, and environmental resistance. The use of isocyanates andpolyurethane (PU) prepolymers represents a more robust solution, with their use being rapidly expanding, despite being a more expensive solution. Isocyanate resins provide properties far superior to those of UF in terms of mechanical properties, better resistance to moisture, and they are free from formaldehyde.

[0005] Isocyanates / PU prepolymers react at room temperature with all organic compounds containing groups with active hydrogens. Examples of groups containing active hydrogens are carboxyl, hydroxyl (including water hydroxyls) and amine groups with hydrogens linked to nitrogen. This property is used by industry to "cure" paints, varnishes, adhesives and artefacts. These systems can be one-component or two- component systems. In one-component systems, curing is carried out by reaction with moisture in the air; in two-component systems, isocyanates / PU prepolymers are mixed, at the time of application, with a polymer containing active groups, such as polyester polyols.

[0006] In particular, the use of isocyanates / PU prepolymers in wooden chipboard is considered a one-component system, but operating as a two-component system - the hardening agents are the hydroxyl groups of wood cellulose and moisture, i.e., in this case the second component is the substrate itself.

[0007] Despite the technical advantages of isocyanates / PU prepolymers systems, unlike UF resins which inherently have a high initial tack (adhesiveness), isocyanates / PU prepolymers systems have low adhesiveness, making it necessary / desirable to add a tackifying agent, preferably an appropriate initial tackifying agent. An initial tackifying agent is a component added to adhesives to enhance their initial tack (or initial adhesion), which is the stickiness of the adhesive when it first contacts the substrate. This property is crucial for applications where the adhesive needs to hold the materials together immediately upon application, even before it has fully cured or set.

[0008] Non-reactive tackifying agents are available on the market, for example hydrocarbon resins. However, these resins are not compatible with isocyanates, i.e. they are not miscible in isocyanate adhesive compositions, so they cannot be used as tackifying agents in compositions containing isocyanates, such as those used in chipboards and wooden laminates. On the other hand, the usual rosin resins aretackifying agents compatible (miscible) with isocyanates, but they do not work in the isocyanates / PU prepolymers system, which shall have a long shelf-life of at least 6 months, since they are reactive with isocyanates, and therefore unstable during storage.

[0009] Almost all rosin-based tackifying agents are resin acids and esters. Resin acids (rosins) contain a carboxylic acid group and therefore active hydrogens that can react with isocyanate. Commercial esters also have reactivity problems, as the residual carboxylic acid is still quite high, and there are still alcohol groups in a sufficiently high concentration to react with isocyanates when mixed and stored for a minimum of 6 months.

[0010] Document WO2016154456 describes compositions that include an ethylene polymer derived from at least one polar monomer with one or more ester groups that polymerize with ethylene, and a rosin ester. The rosin ester may have a low hydroxyl number (for example, a hydroxyl number of six, five or less), a low acid number (for example, an acid number of ten or less), or combinations thereof. The described compositions exhibit high resistance to thermal stress and / or better viscosity stability and / or colour stability after thermal aging and / or better compatibility. However, the use of a rosin ester as a tackifying agent, preferably a green initial tack agent in isocyanate / polyurethane adhesives, wherein the rosin ester is liquid at a temperature greater than -5 °C, preferably liquid at room temperature, is not described.

[0011] Document US 10253215 B2 describes an adhesive composition that is substantially odorless and has a good color and adhesive properties or tack at low temperatures. The adhesive composition comprises a liquid rosin ester compound obtained by reacting a rosin compound with a Cuo monohydric alcohol compound. Although the document describes acrylic adhesive compositions comprising the disclosed liquid rosin ester, that uses a small amount of isocyanate as crosslinked, it is silent on isocyanate adhesives with suitable initial tack comprising said liquid rosin ester.

[0012] Document US 2015 / 232604 Al describes a polymerized rosin compound containing a large amount of a bifunctional rosin dimer component that allows to obtain a linear polymer with a high molecular weight. The polymerized rosincompound can be obtained from a purified rosin methyl ester. The document is however silent on isocyanate adhesive compositions comprising a rosin ester.

[0013] Document CN105907312 describes a preparation method of pale rosin methyl ester with an acid value of 2.1 mg / g. This document is also silent on isocyanate adhesive compositions comprising an initial tackifying agent comprising a rosin ester.

[0014] Document JP2022036653 describes a hot-melt adhesive, in particular an isocyanate / PU prepolymer adhesive comprising a rosin ester. However, this document is silent on thermosetting adhesives, and nothing is disclosed about the initial tack of the adhesive. Indeed, in this document a curing time of 72h is needed to obtain the final pieces.

[0015] There are non-reactive tackifying agents in the state of the art, but they are not compatible with isocyanates / PU prepolymers and therefore cannot be used in isocyanate / PU prepolymer systems. Since they are not miscible with the isocyanates / PU prepolymers, these tackifying agents do not mix properly with the adhesive, making them unsuitable to improve the initial tack of the isocyanate adhesive.

[0016] Rosin resins have good compatibility with a wide spectrum of substances and polymers. However, rosin is mainly comprised of resin acids and, consequently, is reactive towards isocyanates, not meeting the stability requirement. The rosin esters liquid at room temperature existing to date are also reactive with isocyanates, due to a high residual carboxylic acid. As they are reactive with the isocyanates / PU prepolymers, these tackifying agents react with the components of the thermosetting isocyanate adhesives during their storage, making its further application unachievable.

[0017] These facts are described in order to illustrate the technical problem solved by the embodiments of the present document.GENERAL DESCRIPTION

[0018] It is an objective of the present embodiments to provide a solution to the lack of adhesiveness, particularly initial adhesiveness, of isocyanate / PU prepolymer resins.

[0019] In an embodiment, in order to be used in an isocyanate / PU prepolymer system, the tackifying agent (i) cannot have groups reactive with isocyanates, so that the mixture remains stable for at least 6 months (without increased viscosity and / or phase separation); (ii) is compatible with isocyanates / prepolymers; (iii) promotes adhesiveness; and, preferably, (iv) is liquid at room temperature.

[0020] Surprisingly, the rosin esters presented in the present disclosure can be used as tackifying agents, preferably initial tackifying agents (also known as green tack agents), in isocyanate adhesives, in particular isocyanate / PU prepolymer systems, due to their residual and controlled hydroxyl and acid numbers, thus being compatible with thermosetting isocyanate adhesives and not being reactive with isocyanates. This property leads to increased stability of the adhesive, allowing it to be stored on the shelf for at least 6 months. This is not the case of other adhesives using rosin ester- based tackifying agents with acid / hydroxyl numbers higher than those found in the tackifying agent now disclosed.

[0021] The present embodiments are useful for improving the adhesiveness of isocyanate / PU prepolymer resins, in particular the initial tack of the adhesive, without compromising the stability of the resin or its shelf life.

[0022] Within the scope of the present disclosure, the term "tackifying agent" refers to a chemical compound used in adhesive formulations in order to increase their adhesiveness (tack) and the viscosity of the adhesive surface.

[0023] Within the scope of the present disclosure, the term "initial tackifying agent" or "green tack agent" refers to a tackifying agent used in adhesive formulations to provide initial tack before curing, in the gluing process.

[0024] The tackifying agent of the present disclosure is based on the fact that rosin resin esters comprise a content of groups with controlled active hydrogens, i.e., hydroxyl number below 1 mgKOH / g; and an acid number below 4 mgKOH / g, are compatible and non-reactive with isocyanates, and surprisingly provides the adhesive with an improved tack, in particular initial tack.

[0025] In an embodiment, the tackifying agent comprising a rosin ester is liquid at a temperature greater than -5 °C. In a preferred embodiment, the tackifying agent isliquid at room temperature. In another embodiment, the rosin ester does not contain solvents.

[0026] For the scope and interpretation of the present disclosure, it is defined that "room temperature" should be considered as a temperature between 15-30 °C, preferably between 18-25 °C, more preferably between 20-22 °C.

[0027] The present disclosure relates to a thermosetting isocyanate adhesive composition comprising: an initial tackifying agent comprising a rosin ester; and at least one isocyanate compound; wherein the hydroxyl number of the rosin ester is below 1 mgKOH / g, measured by gas chromatography-mass spectrometry with Headspace sampling; the acid number of the rosin ester measured according to the ASTM D465-96:2017 method is below 4 mgKOH / g; and wherein the rosin ester is liquid at a temperature greater than -5 °C, preferably at a temperature greater than 15 °C. Preferably, the thermosetting isocyanate adhesive composition is for glueing wooden materials, such as wooden boards.

[0028] In an embodiment, the isocyanate compound is selected from a list comprising toluene diisocyanate, methylene diphenyl diisocyanate, hexamethylene diisocyanate, or mixtures thereof.

[0029] In an embodiment, the tackifying agent is an initial tackifying agent.

[0030] In an embodiment, the thermosetting isocyanate adhesive composition further comprises at least a polyol, preferably a polyester polyol, more preferably a linear polyester polyol, such as polyols from series Baycoll (COVESTRO; ex: Baycoll® AD 2047).

[0031] In an embodiment, the adhesive is an isocyanate / polyurethane pre-polymer adhesive.

[0032] In an embodiment, the thermosetting isocyanate adhesive composition comprises 1-50% (w / w) of the tackifying agent; and 50-99% (w / w) of the at least one isocyanate compound.

[0033] In an embodiment, the hydroxyl number of the rosin ester ranges between 0.1 to 1 mgKOH / g; and / or the acid number of the rosin ester ranges from 0.1 to 3 mgKOH / g; preferably from 1 to 2 mgKOH / g.

[0034] In an embodiment, the molecular weight of the rosin ester ranges between 290 and 500 Da; preferably between 320 and 400 Da.

[0035] In an embodiment, the disclosed thermosetting isocyanate adhesive composition further comprises pigments, inert matter, or mixtures thereof; preferably up to 9% (w / w) of inert matter wherein the inert matter is selected from a list comprising silica, calcium carbonate, mica, barite, or mixtures thereof.

[0036] In an embodiment, the thermosetting isocyanate adhesive composition is liquid at a temperature greater than -5 °C, preferably at a temperature greater than 15 °C.

[0037] An aspect of the present disclosure relates to an article comprising a first and a second part adhesively bonded by means of the disclosed adhesive composition. Preferably, the first and second part is a first and a second wooden board.

[0038] The present disclosure also describes the use of a rosin ester as a tackifying agent of a thermosetting isocyanate adhesive, wherein the hydroxyl number of the rosin ester is below 1 mgKOH / g, measured by gas chromatography-mass spectrometry with Headspace sampling; the acid number of the rosin ester is below 4 mgKOH / g, measured according to the ASTM D465-96:2017 method; and wherein the rosin ester is liquid at a temperature greater than -5 °C.

[0039] In an embodiment, the tackifying agent is an initial tackifying agent.

[0040] In an embodiment, the hydroxyl number of the rosin ester ranges between 0.1 to 1 mgKOH / g.

[0041] In an embodiment, the acid number of the rosin ester ranges from 0.1 to 3 mgKOH / g; preferably 1 to 2 mgKOH / g.

[0042] In an embodiment, the rosin ester is liquid at a temperature greater than 15 °C.

[0043] In an embodiment, the molecular weight of the rosin ester ranges between 290 and 500 Da; preferably 320 and 400 Da.

[0044] In an embodiment, the viscosity of the rosin ester ranges between 2000 and 100000 mPa.s at 20 °C.

[0045] The present disclosure further describes a tackifying agent for a thermosetting isocyanate adhesive that comprises a rosin ester, wherein the hydroxyl number of therosin ester is below 1 mgKOH / g, measured by gas chromatography-mass spectrometry with Headspace sampling; the acid number of the rosin ester is below 4 mgKOH / g, measured according to the ASTM D465-96:2017 method; and wherein the rosin ester is liquid at a temperature greater than -5 °C.

[0046] In an embodiment, the tackifying agent is an initial tackifying agent.

[0047] In an embodiment, the hydroxyl number of the rosin ester ranges between 0.1 to 1 mgKOH / g.

[0048] In an embodiment, the acid number of the rosin ester is below 3 mgKOH / g, preferably ranging from 0.1 to 3 mgKOH / g; more preferably from 1 to 2 mgKOH / g.

[0049] In an embodiment, the rosin ester is a rosin and methanol ester. In another embodiment the rosin ester is a rosin and ethanol ester, rosin and 1-propanol ester, or rosin and 1-butanol ester.

[0050] In an embodiment, the rosin ester is liquid at a temperature greater than 15 °C.

[0051] In an embodiment, the molecular weight of the rosin ester ranges from 290 to 500 Da, preferably from 320 to 400 Da.

[0052] In an embodiment, the viscosity of the rosin ester ranges between 2000 and 100000 mPa.s at 20 °C.

[0053] The viscosity measurement of the rosin ester can be carried out in several ways; in this disclosure the viscosity measurement was carried out on a Kinexus rheometer using a cone-and-plate geometry (cone diameter: 40 mm; cone angle: 4°; geometry CP 4 / 40) with a cutting rate of 25 s’1, at 20 °C.

[0054] One aspect of the present disclosure relates to an adhesive comprising the rosin ester described. In an embodiment, the adhesive comprises isocyanates and PU prepolymers. In another embodiment, the resin comprises isocyanates, polyurethane prepolymers, or mixtures thereof.

[0055] The present embodiment also relates to an adhesive composition comprising the described tackifying agent, and a compound comprising an isocyanate group.

[0056] In an embodiment, the adhesive composition comprises:1-50% (m / m) of the tackifying agent; and50-99% (m / m) of the compound comprising an isocyanate group.

[0057] In an embodiment, the adhesive composition further comprises pigments, inert matter, or mixtures thereof.

[0058] In an embodiment, the adhesive composition comprises up to 9% (m / m) of inert matter. In a preferred embodiment, the inert matter is selected from a list comprising silica, calcium carbonate, mica, barite, or mixtures thereof.

[0059] In an embodiment, the compound comprising an isocyanate group is selected from a list comprising toluene diisocyanate, methylene diphenyl diisocyanate, hexamethylene diisocyanate, or mixtures thereof, as well as PU prepolymers, such as prepolymers from Desmodur® series (Covestro).

[0060] The present disclosure further describes an article comprising the tackifying agent or adhesive composition described in any of the previous embodiments. Preferably, an article comprising a first and a second part adhesively bonded by means of an adhesive composition as disclosed.

[0061] In an embodiment, the article is a wooden chipboard, wooden laminate, solid wood, or combinations thereof.

[0062] The present disclosure relates to a method for obtaining a rosin ester from a rosin resin, wherein the hydroxyl number is below 1 mgKOH / g, measured by gas chromatography-mass spectrometry with Headspace sampling; the acid number is below 4 mgKOH / g, measured according to the ASTM D465-96:2017 method; and that is liquid at a temperature greater than -5 °C, comprising the following steps:(i) reacting the rosin resin with an excess of volatile alcohol, by esterification, with water removal, preferably at 200 - 280 °C, under pressure at 5900 kPa, for 14 h; preferably, the rosin resin and volatile alcohol are in a molar ratio of 1:100 to 1:8;(ii) removing the residual volatile alcohol;(iii) drying the reacted resin and adding a new excess of volatile alcohol;(iv) repeating steps (i) to (iii) until a rosin ester resin with an acid number of less than 30 mgKOH / g, preferably 20 mgKOH / g, more preferably 18 mgKOH / g is obtained;(v) refining the obtained ester.

[0063] In an embodiment, the rosin resin and volatile alcohol are in a molar ratio of 1:5.

[0064] In an embodiment, the step of removing the volatile alcohol is done by stripping - entrainment with a gas, for example water, nitrogen or carbon dioxide.

[0065] In an embodiment for better results, the ester is refined by fractional distillation, preferably under vacuum.BRIEF DESCRIPTION OF THE FIGURES

[0066] For an easier understanding, figures are herein attached, which represent preferred embodiments that are not intended to limit the object of the present description.

[0067] Figure 1: Schematic representation of the device used to determine the relative initial tack (green tack) of different adhesive samples. 1- vertical support; 2 - arm; 3 - adhesive under test; 4 - pressure applied to the adhesive; 5 - specimen to be glued; 6 - weight; 7 - specimen to be glued.

[0068] Figure 2: Embodiment of results obtained in the relative initial tack (green tack) test. Results presented as falling time in minutes. 1,2 and 4 - results obtained with an embodiment of adhesive samples as described in the present disclosure (with initial tackifying agent comprising a rosin ester) 3 - adhesive without tackifying agent.DETAILED DESCRIPTION

[0069] The present disclosure relates to a thermosetting isocyanate adhesive composition comprising a tackifying agent comprising a rosin ester, the use of a rosin ester as a tackifying agent of a thermosetting isocyanate adhesive, preferably an initial tackifying agent, wherein the hydroxyl number of the rosin ester is below 1 mgKOH / g; the acid number of the rosin ester is below 4 mgKOH / g; and wherein the rosin ester is liquid at a temperature greater than -5 °C. A tackifying agent, preferably an initial tackifying agent, comprising a rosin ester with said characteristics, resins and articlescomprising the described rosin ester, as well as the method of preparing said ester, are also described in the present disclosure.

[0070] The present disclosure also concerns to the use of a rosin ester as a tackifying agent (or tackifier) of an adhesive, preferably an initial tackifying agent (green tack agent), wherein the hydroxyl number of the rosin ester is below 1 mgKOH / g; the acid number of the rosin ester is below 4 mgKOH / g; and wherein the rosin ester is liquid at a temperature greater than -5 °C. A tackifying agent, preferably an initial tackifying agent (a green tack agent), comprising a rosin ester with said characteristics, resins and articles comprising the described rosin ester, as well as the method of preparing said ester, are also described in the present disclosure.

[0071] In an embodiment, the reactivity of rosin resin acids was reduced through their esterification with alcohols; preferably volatile monoalcohols such as methanol, ethanol, 1-propanol and / or 1-butanol and / or mixtures thereof; even more preferably methanol.

[0072] In an embodiment, the rosin ester obtained was refined, in order to eliminate excess acids, by competitive methods, such as vacuum distillation. The use of volatile alcohols in the esterification process allowed the elimination of residual alcohols through stripping processes after esterification.

[0073] In an embodiment, the rosin esters obtained are liquid at room temperature, and do not show reactivity with isocyanates, fulfilling the requirements / preferences for a tackifying agent to be used with thermosetting isocyanate adhesives, in particular isocyanate / polyurethane prepolymer systems.

[0074] In an embodiment, the rosin ester was obtained by esterifying the rosin with a volatile alcohol through a Fisher esterification reaction. In an embodiment, rosin and excess volatile alcohol were mixed, preferably in a molar ratio of 1:5, and heated to a temperature between 250-280 °C, under pressure at 5900 kPa, until the acid number was below 30 mgKOH / g.

[0075] In an embodiment, after esterification, excess methanol is removed through a stripping process. The raw methanol ester, free from free methanol residues, was then subjected to high vacuum distillation, in order to remove the free resin acids, and thuslower the acid number to a maximum value of 4 mgKOH / g. In the distillation process, the refined methanol ester (liquid) is obtained by condensation of the top stream and concentrated resin acids are obtained in the bottom stream, which can be recycled and used in a new esterification process.

[0076] In an embodiment, the acid number was measured by titration with a calibrated alcoholic KOH solution, according to the ASTM D465-96:2017 method; the hydroxyl number was calculated through the residual alcohol content, assessed by gas chromatography-mass spectrometry with Headspace sampling.

[0077] In an embodiment the rosin ester is obtained by the following method:• adding 680 grams of rosin (2 moles of resin acid) and 128 grams of methanol (4 moles), in a 1:2 molar ratio, in an autoclave;• after air removal, closing the autoclave and increasing the temperature to 270 °C, with a pressure increase to 5000-5900 kPa, starting the esterification reaction;• removing the reaction water during esterification using a packing column at the top of the autoclave - as water is generated in the esterification process, the column separates water from methanol. The methanol coming from the top of the column (free from water) is condensed and sent back to the autoclave. The autoclave is maintained at 270 °C until the acid number is below 20 mgKOH / g.• turning off the return of dry methanol to the autoclave, depressurizing the autoclave through the column and collecting the unreacted methanol;• removing residual methanol by stripping with nitrogen at a temperature of 270 °C. Then, reducing the autoclave temperature to 100 °C;• removing the obtained resin from the autoclave and placing it in a vacuum distiller to distill the resin to obtain the described rosin ester.

[0078] In an embodiment, a distilled ester with a maximum acid number of 4 mg / KOH / g and a residue with an acid number of 28 mgKOH / g are obtained.

[0079] In an embodiment, the use of excess alcohol made it possible to obtain an ester with a low acid number. In an embodiment, esterification using a very volatile alcohol,preferably a monoalcohol, makes it possible to completely remove volatile monoalcohol residues after the esterification reaction. Thus, complete removal of excess, unreacted alcohol, for example methanol, ensures the absence of hydroxyl groups in the final product. The several steps of removal of the residual volatile alcohol also improved the complete removal of excess, unreacted alcohol.

[0080] In an embodiment, the rosin ester obtained can be refined by fractional distillation or thin layer, under vacuum, allowing to obtain a methanol ester with a controlled acid number. In a further embodiment, the rosin ester obtained has a hydroxyl number below 1 mgKOH / g, measured by gas chromatography-mass spectrometry with Headspace sampling; an acid number, measured according to the ASTM D465-96:2017 method, below 4 mgKOH / g; and is liquid at a temperature greater than -5 °C, preferably at a temperature greater than 15 °C.

[0081] In an embodiment, the obtained rosin ester was incorporated in a thermosetting isocyanate adhesive, in particular an isocyanate / polyurethane prepolymer system, which are liquid at room temperature. Surprisingly, the obtained adhesive composition has a long shelf life (at least 6 months), due to the compatibility (miscibility) and non-reactivity between the rosin ester and the isocyanate which was not achieved when using other rosin esters. Also, the inclusion of the disclosed rosin ester as a tackifying agent, in particular an initial tackifying agent, lead to a strong initial adhesion (initial tack) of two wooden boards (Figure 2), resulting in a longer falling time, as compared to an adhesive without the rosin ester tackifying agent. Figure 1 shows a schematic representation of an embodiment of a device used to determine the relative initial tack (green tack) of different adhesive samples. In an embodiment, the adhesive under test was applied to a defined area (2x2cm=4cm2) and a certain amount of adhesive / area (25 grams / m2). Substrates (specimens to be glued) 7 and 5 have the same width (2 cm), so the area is defined by the height at which the adhesive is placed. The defined amount of adhesive is applied at a certain height on substrate 5, to which a certain weight (9 g) 6 is attached. After spreading the adhesive on substrate 5, this substrate is pressed against substrate 7 in such a way that contact is made on an equivalent area of this substrate. As soon as the pressure of one substrate on the other ceases (1 to 2 s), timing is started until substrate 5 falls.

[0082] In an embodiment, the slip time until substrate 5 falls is a relative measure of the initial adhesiveness; the longer the time, the greater the initial adhesiveness of the adhesive sample.

[0083] Figure 2 shows an embodiment of the test used to calculate results the relative initial tack of four adhesive samples. Samples 1, 2 and 4 comprise a tackifying agent comprising a rosin ester as described in the present disclosure. Sample 3 does not have the disclosed tackifying agent, resulting in a lower falling time thus, less initial tack.

[0084] In an embodiment, the polyurethane adhesive of the present disclosure can be applied in different articles, such as wooden chipboards, wooden laminates, solid woods, or combinations thereof. In an embodiment of application, the adhesive composition can be applied by spray.

[0085] The term "comprises" or "comprising" when used herein is intended to indicate the presence of stated features, elements, integers, steps and components, but not to preclude the presence or addition of one or more other features, elements, integers, steps and components, or groups thereof.

[0086] The present invention is, of course, in no way restricted to the embodiments described in this document and a person with ordinary skill in the art will foresee many possibilities to modifications thereof and replacing technical characteristics with other equivalent ones, depending on the requirements of each situation, as defined in the attached claims.

[0087] The following claims define further embodiments of the present description.

Claims

C L A I M S1. Thermosetting isocyanate adhesive composition comprising: a tackifying agent comprising a rosin ester; and at least one isocyanate compound; wherein the hydroxyl number of the rosin ester is below 1 mgKOH / g, measured by gas chromatography-mass spectrometry with Headspace sampling; the acid number of the rosin ester measured according to the ASTM D465-96:2017 method is below 4 mgKOH / g; and wherein the rosin ester is liquid at a temperature greater than -5 °C, preferably at a temperature greater than 15 °C.

2. Thermosetting isocyanate adhesive composition according to the preceding claim wherein the isocyanate compound is selected from a list comprising toluene diisocyanate, methylene diphenyl diisocyanate, hexamethylene diisocyanate, or mixtures thereof.

3. Thermosetting isocyanate adhesive composition according to any of the previous claims wherein the tackifying agent is an initial tackifying agent.

4. Thermosetting isocyanate adhesive composition according to any of the previous claims further comprising at least a polyol, preferably a polyester polyol.

5. Thermosetting isocyanate adhesive composition according to any of the previous claims wherein the adhesive is an isocyanate / polyurethane pre-polymer adhesive.

6. Thermosetting isocyanate adhesive according to any of the preceding claims comprising:1-50% (w / w) of the tackifying agent;50-99% (w / w) of the at least one isocyanate compound.

7. Thermosetting isocyanate adhesive composition according to any of the preceding claims wherein the hydroxyl number of the rosin ester ranges between 0.1 to 1mgKOH / g; and / or the acid number of the rosin ester ranges from 0.1 to 3 mgKOH / g; preferably from 1 to 2 mgKOH / g.

8. Thermosetting isocyanate adhesive composition according to any of the preceding claims wherein the molecular weight of the rosin ester ranges between 290 and 500 Da; preferably between 320 and 400 Da.

9. Thermosetting isocyanate adhesive composition according to any of the preceding claims further comprising pigments, inert matter, or mixtures thereof; preferably up to 9% (w / w) of inert matter wherein the inert matter is selected from a list comprising silica, calcium carbonate, mica, barite, or mixtures thereof.

10. Thermosetting isocyanate adhesive composition according to any of the preceding claims wherein the composition is liquid at a temperature greater than -5 °C, preferably at a temperature greater than 15 °C.

11. Article comprising the thermosetting isocyanate adhesive as disclosed in any of the previous claims.

12. Article according to the previous claim wherein the article is a wooden chipboard, wooden laminate, solid wood, or combinations thereof.

13. Use of a rosin ester as a tackifying agent of a thermosetting isocyanate adhesive, wherein the hydroxyl number of the rosin ester is below 1 mgKOH / g measured by gas chromatography-mass spectrometry with Headspace sampling; the acid number of the rosin ester measured according to the ASTM D465-96:2017 method is below 4 mgKOH / g; and wherein the rosin ester is liquid at a temperature greater than -5 °C, preferably at a temperature greater than 15 °C.

14. Use of a rosin ester according to the preceding claim wherein the tackifying agent is an initial tackifying agent.

15. Use of a rosin ester according to any of the preceding claims 12-13 wherein the hydroxyl number ranges between 0.1 to 1 mgKOH / g; and / or the acid number ranges from 0.1 to 3 mgKOH / g; preferably from 1 to 2 mgKOH / g.

16. Use of a rosin ester according to any of the preceding claims 12-14 wherein the molecular weight of the rosin ester ranges between 290 and 500 Da; preferably between 320 and 400 Da.

17. Use of a rosin ester according to any of the preceding claims 12-15 wherein the viscosity of the rosin ester ranges between 2000 and 100000 mPa.s at 20 °C.

18. Tackifying agent for a thermosetting isocyanate adhesive wherein the tackifying agent comprises a rosin ester, wherein the hydroxyl number of the rosin ester is below 1 mgKOH / g measured by gas chromatography-mass spectrometry with Headspace sampling; the acid number of the rosin ester measured according to the ASTM D465-96:2017 method is below 4 mgKOH / g; and wherein the rosin ester is liquid at a temperature greater than -5 °C, preferably at a temperature greater than 15 °C.

19. Tackifying agent according to the preceding claim wherein the tackifying agent is an initial tackifying agent.

20. Tackifying agent according to any of the preceding claims 17-18 wherein the hydroxyl number of the rosin ester ranges between 0.1 to 1 mgKOH / g; and / or wherein the acid number of the rosin ester is below 3 mgKOH / g, preferably the acid number of the rosin ester ranges from 0.1 to 3 mgKOH, more preferably the acid number of the rosin ester ranges from 1 to 2 mgKOH / g.

21. Tackifying agent according to any of the preceding claims 17-19 wherein the molecular weight of the rosin ester ranges from 290 to 500 Da; preferably from320 to 400 Da.

22. Tackifying agent according to any of the preceding claims 17-20 wherein the viscosity of the rosin ester ranges between 2000 and 100000 mPa.s at 20 °C.

23. Method for obtaining a rosin ester from a rosin resin, wherein the hydroxyl number is below 1 mgKOH / g, measured by gas chromatography-mass spectrometry with Headspace sampling; the acid number is below 4 mgKOH / g, measured according to the ASTM D465-96:2017 method; and that is liquid at a temperature greater than -5 °C, comprising the following steps:(i) reacting the rosin resin with an excess of volatile alcohol, by esterification, with water removal, preferably at 200 - 280 °C for 14 h;(ii) removing the residual volatile alcohol;(iii) drying the reacted resin and adding a new excess of volatile alcohol;(iv) repeating steps (i) to (iii) until a rosin ester resin with an acid number of less than 30 mgKOH / g, preferably 20 mgKOH / g, more preferably 18 mgKOH / g is obtained;(v) refining the obtained ester, in particular by fractional distillation or thin layer, preferably under vacuum; wherein the rosin resin and the volatile alcohol are in a molar ratio of 1:100 to 1:2; and wherein the step of removing the volatile alcohol is done by stripping.

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